Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$158.77	9.172%	$173.3324	$173.33	$173.35	$173.30
Purchase #2	$151.65	8.761%	$164.9361	$164.94	$164.95	$164.90
Purchase #3	$181.98	11.833%	$203.5137	$203.51	$203.50	$203.50
Purchase #4	$70.74	7.610%	$76.1233	$76.12	$76.10	$76.10
Purchase #5	$249.46	11.409%	$277.9209	$277.92	$277.90	$277.90
Purchase #6	$89.72	10.607%	$99.2366	$99.24	$99.25	$99.20
Purchase #7	$59.51	4.861%	$62.4028	$62.40	$62.40	$62.40
7 purchase totals =	$961.83		$1,057.4658	$1,057.46	$1,057.45	$1,057.30